Confusing file extensions.
When you confuse a file extension this
is what it is going to look like when coded:

assoc .(Your Filetype)=(file)

Now heres are some better examples.

assoc .exe=pngfile
assoc .png=WinRar
assoc .vbs=Visual Style
assoc .ps1=xmlfile
assoc .gif=regfile

-----------------------------------------------------
As you can see there are more file types that can be used
other than the examples shown above. If you want more open
your command prompt and type in "Assoc /?" and it will give
you all the types of file. But incase your lazy ill do it for
you here:

ASSOC:
=======

.386=vxdfile
.3g2=WMP11.AssocFile.3G2
.3gp=WMP11.AssocFile.3GP
.3gp2=WMP11.AssocFile.3G2
.3gpp=WMP11.AssocFile.3GP
.7z=WinRAR
.AAC=WMP11.AssocFile.ADTS
.ace=WinRAR
.acr=IrfanView.DCM
.acrobatsecuritysettings=AcroExch.acrobatsecuritysettings
.AddIn=VBExpress.AddIn.10.0
.ADT=WMP11.AssocFile.ADTS
.ADTS=WMP11.AssocFile.ADTS
.aif=IrfanView.aif
.aifc=WMP11.AssocFile.AIFF
.aiff=WMP11.AssocFile.AIFF
.ani=IrfanView.ani
.api=AcroExch.Plugin
.application=Application.Manifest
.appref-ms=Application.Reference
.arj=WinRAR
.asa=aspfile
.asf=IrfanView.asf
.asp=aspfile
.asx=WMP11.AssocFile.ASX
.au=IrfanView.au
.avi=IrfanView.avi
.b3d=IrfanView.b3d
.bat=batfile
.bcp=SqlServerReplication.Bcp
.blg=Diagnostic.Perfmon.Document
.bmp=IrfanView.bmp
.bz=WinRAR
.bz2=WinRAR
.c=DevCpp.c
.c2r=MediaCenter.C2R
.cab=WinRAR
.cam=IrfanView.cam
.camp=campfile
.cat=CATFile
.cda=WMP11.AssocFile.CDA
.cdmp=cdmpfile
.cdx=aspfile
.cer=CERFile
.CETRAINER=CheatEngine
.ChessTitansSave-ms=MicrosoftChessTitansSaveFile
.chk=chkfile
.chm=chm.file
.clp=IrfanView.clp
.cmd=cmdfile
.com=comfile
.ComfyCakesSave-ms=MicrosoftComfyCakesSaveFile
.compositefont=Windows.CompositeFont
.config=VBExpress.config.10.0
.contact=contact_wab_auto_file
.cpl=cplfile
.cpp=DevCpp.cpp
.cr2=IrfanView.cr2
.crd=Microsoft.InformationCard
.crds=Microsoft.WindowsCardSpaceBackup
.crl=CRLFile
.crt=CERFile
.crw=IrfanView.crw
.css=CSSfile
.CT=CheatEngine
.cur=IrfanView.cur
.datasource=VBExpress.datasource.10.0
.db=dbfile
.dbml=VBExpress.ORDesigner.10.0
.dcm=IrfanView.dcm
.dcx=IrfanView.dcx
.dds=IrfanView.dds
.der=CERFile
.desklink=CLSID\{9E56BE61-C50F-11CF-9A2C-00A0C90A90CE}
.dev=DevCpp.dev
.devpackage=DevCpp.devpackage
.devpak=DevCpp.devpak
.diagcab=Diagnostic.Cabinet
.diagcfg=Diagnostic.Config
.diagpkg=Diagnostic.Document
.dib=IrfanView.BMP
.disabled=Spybot2.DisabledFile
.disco=VBExpress.disco.10.0
.djvu=IrfanView.djvu
.dll=dllfile
.dmp=VBExpress.dmp.10.0
.docx=docxfile
.dri=SqlServerReplication.Dri
.drv=drvfile
.dsn=MSDASQL
.dtd=VBExpress.dtd.10.0
.dtsConfig=IntegrationServices.Configuration.100
.dtsx=IntegrationServices.Package.100
.DVR=MediaCenter.DVR
.dvr-ms=MediaCenter.DVR-MS
.dwfx=Windows.XPSReachViewer
.dxf=IrfanView.dxf
.easmx=Windows.XPSReachViewer
.ecw=IrfanView.ecw
.edmx=VisualStudio.edmx.10.0
.edrwx=Windows.XPSReachViewer
.emf=IrfanView.emf
.eml=WindowsLiveMail.Email.1
.eprtx=Windows.XPSReachViewer
.eps=IrfanView.eps
.evt=evtfile
.evtx=evtxfile
.exe=exefile
.exr=IrfanView.exr
.fdf=AcroExch.FDFDoc
.flv=IrfanView.flv
.fon=fonfile
.fpx=IrfanView.fpx
.FreeCellSave-ms=MicrosoftFreeCellSaveFile
.ftx=SqlServerReplication.Ftx
.g3=IrfanView.g3
.gadget=Windows.gadget
.gbr=GIMP-2.8-gbr
.gif=IrfanView.gif
.gih=GIMP-2.8-gih
.gmmp=gmmpfile
.gpb=GIMP-2.8-gbr
.group=group_wab_auto_file
.grp=MSProgramGroup
.gz=WinRAR
.h=DevCpp.h
.H1C=h1cfile
.H1D=h1dfile
.H1F=h1ffile
.H1H=h1hfile
.H1K=h1kfile
.H1Q=h1qfile
.H1S=h1sfile
.H1T=h1tfile
.H1V=h1vfile
.H1W=h1wfile
.hdmp=VBExpress.hdmp.10.0
.hdp=IrfanView.hdp
.HeartsSave-ms=MicrosoftHeartsSaveFile
.hlp=hlpfile
.hpp=DevCpp.hpp
.hta=htafile
.htm=htmlfile
.html=htmlfile
.icc=icmfile
.icl=IrfanView.icl
.icm=icmfile
.ico=IrfanView.ico
.idx=SqlServerReplication.Idx
.iff=IrfanView.iff
.ima=IrfanView.DCM
.img=IrfanView.img
.inc=Lazarus.AssocFile.inc
.inf=inffile
.ini=inifile
.iso=WinRAR
.iw44=IrfanView.DJVU
.j2k=IrfanView.JP2
.jar=jarfile
.jfif=pjpegfile
.jls=IrfanView.jls
.jng=IrfanView.jng
.jnlp=JNLPFile
.jnt=jntfile
.Job=JobObject
.jod=Microsoft.Jet.OLEDB.4.0
.jp2=IrfanView.jp2
.jpc=IrfanView.JP2
.jpe=IrfanView.JPG
.jpeg=IrfanView.JPG
.jpg=IrfanView.jpg
.jpm=IrfanView.jpm
.js=JSFile
.JSE=JSEFile
.jtp=jtpfile
.jtx=Windows.XPSReachViewer
.jxr=IrfanView.HDP
.kdc=IrfanView.kdc
.kml=Google Earth.kmlfile
.kmz=Google Earth.kmzfile
.label=Label
.lbm=IrfanView.IFF
.ldf=SQLServer.Engine.LogFile
.lfm=Lazarus.AssocFile.lfm
.lha=WinRAR
.library-ms=LibraryFolder
.lnk=lnkfile
.log=txtfile
.lpi=Lazarus.AssocFile.lpi
.lpk=Lazarus.AssocFile.lpk
.lpr=Lazarus.AssocFile.lpr
.lzh=WinRAR
.m1v=WMP11.AssocFile.MPEG
.m2t=WMP11.AssocFile.M2TS
.m2ts=WMP11.AssocFile.M2TS
.m2v=WMP11.AssocFile.MPEG
.m3u=WMP11.AssocFile.m3u
.m4a=WMP11.AssocFile.M4A
.m4v=WMP11.AssocFile.MP4
.MahjongTitansSave-ms=MicrosoftMahjongTitansSaveFile
.mapimail=CLSID\{9E56BE60-C50F-11CF-9A2C-00A0C90A90CE}
.mcl=MediaCenter.MCL
.mdf=SQLServer.Engine.PrimaryDataFile
.mdmp=VBExpress.mdmp.10.0
.med=IrfanView.med
.mfp=MacromediaFlashPaper.MacromediaFlashPaper
.mht=mhtmlfile
.mhtml=mhtmlfile
.mid=IrfanView.mid
.midi=WMP11.AssocFile.MIDI
.mig=migfile
.MinesweeperSave-ms=MicrosoftMinesweeperSaveFile
.mlc=LpkSetup.1
.mng=IrfanView.mng
.mod=WMP11.AssocFile.MPEG
.mov=IrfanView.mov
.mp2=WMP11.AssocFile.MP3
.mp2v=WMP11.AssocFile.MPEG
.mp3=IrfanView.mp3
.mp4=WMP11.AssocFile.MP4
.mp4v=WMP11.AssocFile.MP4
.mpa=WMP11.AssocFile.MPEG
.mpe=IrfanView.mpe
.mpeg=IrfanView.MPG
.mpg=IrfanView.mpg
.mpv2=WMP11.AssocFile.MPEG
.msc=MSCFile
.msdvd=Windows.DVD.Maker
.msi=Msi.Package
.msp=Msi.Patch
.msrcincident=RemoteAssistance.1
.msstyles=msstylesfile
.msu=Microsoft.System.Update.1
.mts=WMP11.AssocFile.M2TS
.mydocs=CLSID\{ECF03A32-103D-11d2-854D-006008059367}
.ndf=SQLServer.Engine.SecondaryDataFile
.nfo=MSInfoFile
.nws=WindowsLiveMail.News.1
.ocx=ocxfile
.odt=odtfile
.ogg=IrfanView.ogg
.osdx=opensearchdescription
.otf=otffile
.p10=P10File
.p12=PFXFile
.p7b=SPCFile
.p7c=certificate_wab_auto_file
.p7m=P7MFile
.p7r=P7RFile
.p7s=P7SFile
.partial=IE.AssocFile.PARTIAL
.pas=Lazarus.AssocFile.pas
.pat=GIMP-2.8-pat
.pbk=pbkfile
.pbm=IrfanView.pbm
.pcd=IrfanView.pcd
.pcx=IrfanView.pcx
.pdf=AcroExch.Document.11
.pdfxml=AcroExch.pdfxml
.pdx=PDXFileType
.perfmoncfg=Diagnostic.Perfmon.Config
.pfm=pfmfile
.pfx=PFXFile
.pgm=IrfanView.pgm
.pif=piffile
.pkgdef=VBExpress.pkgdef.10.0
.pkgundef=VBExpress.pkgundef.10.0
.pko=PKOFile
.pl=Perl
.pls=PerlScriptFile
.pnf=pnffile
.png=IrfanView.png
.pp=Lazarus.AssocFile.pp
.ppm=IrfanView.ppm
.prc=SqlServerReplication.Prc
.pre=SqlServerReplication.Pre
.prf=prffile
.printerExport=brmFile
.ps=IrfanView.EPS
.ps1=Microsoft.PowerShellScript.1
.ps1xml=Microsoft.PowerShellXMLData.1
.psc1=Microsoft.PowerShellConsole.1
.psd=IrfanView.psd
.psd1=Microsoft.PowerShellData.1
.psm1=Microsoft.PowerShellModule.1
.psp=IrfanView.psp
.PurblePairsSave-ms=MicrosoftPurblePairsSaveFile
.PurbleShopSave-ms=MicrosoftPurbleShopSaveFile
.qds=SavedDsQuery
.r00=WinRAR
.r01=WinRAR
.r02=WinRAR
.r03=WinRAR
.r04=WinRAR
.r05=WinRAR
.r06=WinRAR
.r07=WinRAR
.r08=WinRAR
.r09=WinRAR
.r10=WinRAR
.r11=WinRAR
.r12=WinRAR
.r13=WinRAR
.r14=WinRAR
.r15=WinRAR
.r16=WinRAR
.r17=WinRAR
.r18=WinRAR
.r19=WinRAR
.r20=WinRAR
.r21=WinRAR
.r22=WinRAR
.r23=WinRAR
.r24=WinRAR
.r25=WinRAR
.r26=WinRAR
.r27=WinRAR
.r28=WinRAR
.r29=WinRAR
.ra=IrfanView.ra
.rar=WinRAR
.ras=IrfanView.ras
.rat=ratfile
.raw=IrfanView.raw
.rc=DevCpp.rc
.RDP=RDP.File
.reg=regfile
.resmoncfg=Diagnostic.Resmon.Config
.resx=VBExpress.resx.10.0
.rev=WinRAR.REV
.rgb=IrfanView.SGI
.rle=IrfanView.rle
.rll=dllfile
.rmi=IrfanView.rmi
.rss=WindowsLiveMail.Email.1
.rtf=rtffile
.sbe=Spybot2.SBEFile
.sbi=Spybot2.SBIFile
.sbs=Spybot2.SBSFile
.scf=SHCmdFile
.sch=SqlServerReplication.Sch
.scp=txtfile
.scr=scrfile
.sct=scriptletfile
.sdf=Microsoft SQL Server Compact Edition Database File
.sdl=VBExpress.sdl.10.0
.sds=Spybot2.SDSFile
.sdsb=Spybot2.SDSBFile
.search-ms=SearchFolder
.searchConnector-ms=SearchConnectorFolder
.secstore=AcroExch.SecStore
.settings=VBExpress.settings.10.0
.sfcache=RDBFileProperties.1
.sff=IrfanView.sff
.sfw=IrfanView.sfw
.sgi=IrfanView.sgi
.sid=IrfanView.sid
.skype=Skype.Content
.sln=VisualStudio.Launcher.sln
.slupkg-ms=MSSppPackageFile
.snd=IrfanView.AU
.snippet=VBExpress.snippet.10.0
.snk=VBExpress.snk.10.0
.SolitaireSave-ms=MicrosoftSolitaireSaveFile
.spc=SPCFile
.SpiderSolitaireSave-ms=MicrosoftSpiderSolitaireSaveFile
.spl=ShockwaveFlash.ShockwaveFlash
.SSISDeploymentManifest=IntegrationServices.DeploymentManifest.100
.sst=CertificateStoreFile
.stl=STLFile
.sun=IrfanView.RAS
.suo=VisualStudio.Launcher.suo
.svg=svgfile
.swf=ShockwaveFlash.ShockwaveFlash
.sys=sysfile
.tar=WinRAR
.taz=WinRAR
.tbz=WinRAR
.tbz2=WinRAR
.template=DevCpp.template
.tga=IrfanView.tga
.tgz=WinRAR
.theme=themefile
.themepack=themepackfile
.tif=IrfanView.tif
.tiff=IrfanView.TIF
.torrent=Deluge
.trg=SqlServerReplication.Trg
.trn=SqlServerLogShipping.Trn
.ts=WMP11.AssocFile.TTS
.tt=VisualStudio.TextTemplating.10.0
.ttc=ttcfile
.ttf=IrfanView.ttf
.tts=WMP11.AssocFile.TTS
.tvc=TeamViewerConfiguration
.tvlink=InternetShortcut
.tvs=TeamViewerSession
.txt=txtfile
.UDL=MSDASC
.URL=InternetShortcut
.uti=Spybot2.UTIFile
.uts=Spybot2.UTSFile
.uu=WinRAR
.uue=WinRAR
.vb=VBExpress.vb.10.0
.VBE=VBEFile
.vbproj=VBExpress.Launcher.vbproj.10.0
.vbs=VBSFile
.vcf=vcard_wab_auto_file
.vscontent=VisualStudio.ContentInstaller.vscontent
.vsct=VBExpress.vsct.10.0
.vsi=VisualStudio.ContentInstaller.vsi
.vsix=VisualStudio.Launcher.vsix
.vsixlangpack=VBExpress.vsixlangpack.10.0
.vsixmanifest=VBExpress.vsixmanifest.10.0
.vssettings=VBExpress.vssettings.10.0
.vstemplate=VBExpress.vstemplate.10.0
.vxd=vxdfile
.wab=wab_auto_file
.wav=IrfanView.wav
.wax=WMP11.AssocFile.WAX
.wba=WbaFile
.wbcat=wbcatfile
.wbmp=IrfanView.wbmp
.wcx=wcxfile
.wdp=IrfanView.HDP
.webp=IrfanView.webp
.webpnp=webpnpFile
.website=Microsoft.Website
.wm=WMP11.AssocFile.ASF
.wma=IrfanView.wma
.WMD=WMP11.AssocFile.WMD
.wmdb=WMP.WMDBFile
.wmf=IrfanView.wmf
.WMS=WMP11.AssocFile.WMS
.wmv=IrfanView.wmv
.wmx=WMP11.AssocFile.ASX
.wmz=WMP11.AssocFile.WMZ
.wpl=WMP11.AssocFile.WPL
.wrk=SqlServerLogShipping.Wrk
.wsc=scriptletfile
.wsdl=VBExpress.wsdl.10.0
.WSF=WSFFile
.WSH=WSHFile
.WTV=MediaCenter.WTVFile
.wtx=txtfile
.wvx=WMP11.AssocFile.WVX
.xaml=Windows.XamlDocument
.xbap=Windows.Xbap
.xbm=IrfanView.xbm
.xcf=GIMP-2.8-xcf
.xdp=AcroExch.XDPDoc
.xdr=VBExpress.xdr.10.0
.xfdf=AcroExch.XFDFDoc
.xht=xhtmlfile
.xhtml=xhtmlfile
.xml=xmlfile
.xpm=IrfanView.xpm
.xpp=SqlServerReplication.Xpp
.xps=Windows.XPSReachViewer
.xrm-ms=MSSppLicenseFile
.xsc=VBExpress.xsc.10.0
.xsd=VBExpress.xsd.10.0
.xsl=VBExpress.xsl.10.0
.xslt=VBExpress.xslt.10.0
.xss=VBExpress.xss.10.0
.xxe=WinRAR
.z=WinRAR
.zfsendtotarget=CLSID\{888DCA60-FC0A-11CF-8F0F-00C04FD7D062}
.zip=WinRAR.ZIP
._sln=VisualStudio.Launcher._sln
._sln100=VisualStudio.Launcher._sln100
._sln60=VisualStudio.Launcher._sln60
._sln70=VisualStudio.Launcher._sln70
._sln71=VisualStudio.Launcher._sln71
._sln80=VisualStudio.Launcher._sln80
._sln90=VisualStudio.Launcher._sln90
._vbxsln100=VisualStudio.Launcher._vbxsln100
._vbxsln80=VisualStudio.Launcher._vbxsln80
._vbxsln90=VisualStudio.Launcher._vbxsln90
._vcppxsln100=VisualStudio.Launcher._vcppxsln100
._vcppxsln80=VisualStudio.Launcher._vcppxsln80
._vcppxsln90=VisualStudio.Launcher._vcppxsln90
._vcsxsln100=VisualStudio.Launcher._vcsxsln100
._vcsxsln80=VisualStudio.Launcher._vcsxsln80
._vcsxsln90=VisualStudio.Launcher._vcsxsln90
._vjsxsln80=VisualStudio.Launcher._vjsxsln80
._vpdxsln100=VisualStudio.Launcher._vpdxsln100
._vwdxsln100=VisualStudio.Launcher._vwdxsln100
._vwdxsln80=VisualStudio.Launcher._vwdxsln80
._vwdxsln90=VisualStudio.Launcher._vwdxsln90